As if any sane, thinking person really needed another reason to believe in evolution: this is the most exciting thing I’ve read about HIV research in a long time.

A gene, TRIM5, that provides immunity to retroviruses has been identified in two different primates on opposite ends of the world. Pigtail macaques live primarily in Southeast Asia, owl monkeys only in Central and South America.

Here’s an excerpt:

First, they determined that pigtail macaque cells could fight off other retroviruses, such as the simian and feline relatives of HIV. Then, Bieniasz and Hatziioannou added cyclosporin, a drug that interacts with cyclophilin, to the equation and looked to see whether it affected the pigtail cells’ viral interactions. (The drug is known to overcome the ability of owl-monkey TRIMcyp to fight off the virus.) Sure enough, cyclosporin affected their capacity to fight off the simian and feline retroviruses. “That suggested to us that there was, perhaps, a protein like the owl-monkey TRIMcyp in these monkeys,” Hatziioannou says.

The researchers isolated the pigtail macaques’ TRIM5 gene and found that, like the owl monkeys, the pigtails also had cyclophilin inserted into their TRIM5 gene, though it was found at a slightly different location. Not only that, but there’s a single amino acid change in the pigtail cyclophilin, a tiny modification that appears to dictate whether or not the monkeys can inhibit HIV.